This invention relates generally to unit fuel injectors that perform cyclic fuel pressurization, and more particularly to reverse flow check valves in unit fuel injectors.
Reverse flow check valve assemblies for unit fuel pump-injectors are known, for example U.S. Pat. No. 4,527,738 to Martin issued Jul. 9, 1985, U.S. Pat. No. 4,392,612 to Deckard et al. issued Jul. 12, 1983, and U.S. Pat. No. 5,287,838 to Wells issued Feb. 22, 1994. The function of such check valve assemblies is generally to permit communication of high pressure fuel from a pressurization chamber to a nozzle chamber during an injection phase, and to prevent fluid communication (i.e., reverse flow) of engine cylinder combustion gas from the injection nozzle to the pressurization chamber during a non-injection phase.
The check valve assemblies of Martin and Deckard each include a movable one-way flow check in the form of an imperforate plate, positioned at the end of or adjacent to pressurization sections of their respective fuel injectors. A flow path for pressurized fuel during injection is defined by an annular clearance between the outer periphery of the check and a wall of a bore in which the check is positioned.
With these reverse flow check valve assemblies the plate must be relatively loose in its bore, providing a relatively large clearance in order to provide a cross-sectional flow area that permits sufficient injection fuel flow. One problem that may occur with the relatively loose annular clearance is that the movable check may become cocked or tilted in its bore. Undesirable wear results as the cocked check moves back and forth between upper and lower seats.
Another problem with the above check valve assemblies is that they may not fit in some unit fuel pump-injectors if space is limited. For example, U.S. Pat. No. 5,121,730 to Ausman et al. issued Jun. 16, 1992, and the patent to Wells, illustrate that available space for a reverse flow check valve assembly beneath the pressurization chamber may be limited and would have to be offset with respect to the pressurization chamber axis due to the location and proximity of a fuel inlet check leading to the pressurization chamber. Wells also addresses the problem of xe2x80x9ccockingxe2x80x9d by adding a central hole in the flow check.
In order to provide a reverse flow check valve for the pump-injector of Ausman et al. using a reverse flow check valve similar to those shown in Martin or Deckard et al., the displacement or lift of the check may have to be increased to provide sufficient fuel flow. Such an increase in lift may prevent such reverse flow check valve assemblies from fitting within the limited space available. In the reverse flow check valve assembly taught by Wells, space constraints cause the upper stop to be thin, which could cause structural weakness.
The invention is directed to addressing one or more of the above topics.
In one aspect of the invention, a fuel injector comprises a pressurization section and a nozzle section. The pressurization section at least partially defines a variable-volume pressurization chamber. The nozzle section has a check bore, a nozzle chamber, an orifice, a fuel injection check extending into the nozzle chamber, and a reverse flow check valve fluidly connected with the nozzle chamber.
The fuel injection check is slidably disposed in the check bore between a first position that blocks fluid communication between the nozzle chamber and the orifice and a second position that opens fluid communication between the nozzle chamber and the orifice. A fuel passage fluidly connects the pressurization chamber in the pressurization section with the reverse flow check valve in the nozzle section.
The reverse flow check valve includes a perforated reverse flow check hydraulically movable between an open position that allows fluid communication from the fuel passage to the nozzle chamber and a closed position that denies fluid communication from the nozzle chamber to the fuel passage.
In a second aspect of the invention, a fuel injector comprises a variable-volume pressurization chamber, a nozzle including a nozzle chamber and an orifice, and a reverse flow check valve including a reverse flow check and a column extending through a perforation in the reverse flow check. The reverse flow check is movable between an open position providing fluid communication between the pressurization chamber and the nozzle chamber, and a closed position that blocks fluid communication between the pressurization chamber and the nozzle chamber.
In a third aspect of the invention, a fuel injection method comprises pressurizing fuel in a pressurization chamber within a fuel injector, injecting the pressurized fuel by opening a flow path between the pressurization chamber and an orifice in the fuel injector, and hydraulically moving a reverse flow check axially along a column that extends through a perforation in the reverse flow check to a closing position to close the flow path while fuel injection is not taking place. Opening the flow path comprises hydraulically moving the reverse flow check away from the closing position.